A sugar is a carbohydrate that is sweet to taste. Sugars are used in food and drink as a source of sweetness and energy and are important in biochemistry. Sucrose, also called “table sugar,” is a white crystalline solid. Sucrose is a disaccharide composed of two monosaccharides, glucose and fructose, joined together by a 1→2-α,β-glycosidic bond. Sucrose is commercially extracted from either sugar cane or sugar beet and then purified and crystallized. Other commercial sources are sorghum, date palm, and sugar maples. The monosaccharides, such as glucose (which is produced from sucrose by enzymes or acid hydrolysis), are a store of energy that is used by biological cells. Oxidation of glucose is known as glycolysis. It occurs in virtually all cells. Glucose is oxidized to either lactate or pyruvate. Under aerobic conditions, the dominant product in most tissues is pyruvate and the pathway is known as aerobic glycolysis. When oxygen is depleted, as for instance during prolonged vigorous exercise, the dominant glycolytic product in many tissues is lactate and the process is known as anaerobic glycolysis. Other sugars besides glucose, such as fructose, can enter glycolysis after being converted to appropriate intermediates that can enter the pathway. Glycolysis results in production of NADH and ATP. The NADH generated during glycolysis is used to fuel mitochondrial ATP synthesis via oxidative phosphorylation. ATP powers virtually every activity of the cell and organism. Organisms from the simplest bacteria to humans use ATP as their primary energy currency.